Long pauses on BT devices at end of songs

[JedJ]

On my newish phone (OnePlus 3), Spotify stops playing at the end of a track (apparently randomly) and then remains silent for a few minutes, up to 10 or so, only to resume playing the next song on the album or playlist. If I wake up the phone, the next song starts right up. Spotify with the same phone doesn't do this with BT headphones, but with two different Bose BT speakers. I've checked that it's showing notifications even when the phone is asleep. It is. Any other ideas?

Thanks!

Android 6.0.1
Internal storage 64g
No SD card slot.